234MO - Explaining the relationships between age, endocrine therapy persistence and risk of recurrence in hormone-positive early breast cancer: A nationwide cohort study

Background

Young age is associated with increased risk of recurrence in hormone receptor (HR)-positive early breast cancer (eBC). Lack of adherence to endocrine therapy (ET) has been hypothesized as a reason for the lower survival rates observed in younger patients, but the potential survival benefits of improving adherence to ET in young patients remains unknown.

Methods

In this nationwide cohort study, we used data from the French National Health Data System and causal inference methods to estimate the potential gains in 5-year disease-free survival (DFS) achievable by improving ET persistence in different age groups of women diagnosed with HR-positive eBC. We tested three definitions of ET persistence, which allowed treatment breaks of 30, 90, or 180 days.

Results

A total of 121,852 patients with HR-positive eBC were included in the analyses, of whom 29.9% were younger than 50 years and 1.8% were younger than 34 years at diagnosis. Younger patients had lower DFS and were more likely to discontinue ET than older patients. In patients diagnosed before age 34, strict ET persistence (no 30-day break) improved 5-year DFS rates from 75.8% to 81.4% (5.6 percentage-points, 95% CI: 2.5-8.8) compared to observed persistence. ET persistence strategies allowing for 90- and 180-day breaks reduced the 5-year DFS benefit in this subgroup of patients to 1.3 (95% CI: 0.0-2.5) and 1.9 (95% CI: 0.4-3.5) percentage-points, respectively, compared to observed persistence. In contrast, DFS benefits of improved ET persistence in older patients did not exceed 1.2 percentage-points, compared to observed persistence, regardless of the persistence definition.

Conclusions

The survival benefit that could be achieved with strict ET persistence in women below 34 years with HR-positive eBC highlights the need for tailored strategies to improve ET persistence in this population.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

French National Cancer Institute (INCa), M.

Disclosure

All authors have declared no conflicts of interest.